1. Field of the Invention
The present invention relates to a tape reel of a cassette tape such as video cassette tape.
2. Prior Art
FIG. 5 illustrates an axial section of a central portion of a conventional tape reel, in which reference numerals 10 and 12 designate a hub and an upper flange of the tape reel, respectively. The hub 10 and the upper flange 12 are formed of a synthetic resin. The reference numeral 14 indicates a leaf spring mounted at one end to a cassette casing (not shown) for urging at the other end a pivot 16 which is integrally formed with the center of the upper face 18 of the hub 10.
There is a possibility of wearing of the pivot 16 by the leaf spring 14 since the tape reel is rotated at a high speed during traveling of the tape. To reduce this possibility, a polyacetal resin which is excellent in wear resistance is used for the hub 10. Polyacetal resins are however poor in molding productivity and expensive as compared to styrene resins.
For these reasons, an attempt has been made in which a hub 20 is made of a styrene resin, and a separate pivot 22, made of a polyacetal resin, is placed concentrically on the top face of the hub 20 as illustrated in FIGS. 6(A) and 6(B). The pivot 22 includes a head portion 23 and a circumferential flange 25 projecting radially outwards from the lower end of the head portion 23. The pivot 22 is sandwiched at its circumferential flange 25 between the hub 20 and an upper flange 24 for holding it in position. More specifically, the upper flange 24 has an inverted, generally funnel-shaped center through hole 27 formed through it and a rim 24B defining an upper wall 24A of the center through hole 27. The circumferential flange 25 of the pivot 22 is sandwiched between the rim 24B of the upper flange 24 and the top face of the hub 20. The pivot 22 is urged at its head portion 23 toward the top face of the hub 20 by the leaf spring 14. The pivot 22 is small in volume as compared to the hub 20 and hence use of a polyacetal resin for the hub 20 does not considerably affect both the productivity and the cost of the tape reel.
For assembling the tape reel of FIG. 6, firstly the pivot 22 is placed concentrically on the top face of the hub 20, secondly the upper flange 24 is disposed over the top face of the hub 20 so as to sandwich the pivot 22, and finally the hub 20 and the upper flange 24 are joined together by ultrasonic welding. During handling of the hub 20 with the pivot 22 on it for assembling it to the upper flange 24 in the assembly line, the pivot 22 is liable to slip out of the hub 20 and be lost or to dislodge from the concentric position of the hub 20.
For solving such problems during transportation of the hub with a pivot, other attempts have been made in which pivots are temporarily secured to respective hubs by resiliently holding the former to the latter.
One typical attempt is shown in FIGS. 7A and 7B, in which the hub 26 is provided at the center of its top face with an axial through hole 28, into which is resiliently fitted a boss 32 of a pivot 30. The provision of the axial through hole 28 does not pose a problem in fitting of the boss 32 of the pivot 30 but it raises a problem to the molding of the hub 26: that is, for producing the hub 26 it would be necessary to provide a gate on the mold for injecting a molten resin from the center portion of the mold with respect to the hub 26 but it is not possible to do so in the presence of the axial through hole 28.
In the prior art tape reel in FIGS. 8A and 8B, a hub 34 is provided on its top face with a boss 36, and a pivot 38 has a blind hole 40 formed on the bottom face thereof. The shape of the hub 34 requires a draft (taper for removing a work from tis mold) to be provided to the circumferential face of the boss 36 for molding the hub 34 whereas another draft must be provided to the inner circumferential face of the blind hole 40 of the pivot 38 as well. When the boss 36 is fitted into the blind hole 40, no clutching effect is produced because of the two drafts of same orientation, and thus holding the pivot 38 on the hub 34 is not secure. In addition, it is not easy to examine by visual inspection whether or not the pivot 38 is securely fitted around the boss 36.
Accordingly, it is an object of the present invention to provide a tape reel of a cassette tape which solves the above-mentioned problems.